Stratum having release properties and method of making

ABSTRACT

A stratum having accurately predictable and controllable release properties toward normally tacky and pressure-sensitive adhesive sheet materials is prepared by reacting two moieties, one terminated with a plurality of isocyanate groups and the other a liquid hydroxyl- or amine-containing organosilicone. The hydroxyl or amine groups are at least three carbon atoms distant from the nearest silicone atom and constitute no more than about 4% by weight of the organosilicone. Depending upon the release characteristics achieved, the reaction product can function as a shaped article, all or part of a release liner, or as a low-adhesion backsize for pressure-sensitive adhesive tape.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of copending application Ser. No.423,706, filed Dec. 11, 1973, now U.S. Pat. No. 3,957,724.

BACKGROUND OF THE INVENTION

This invention relates to polymers which exhibit release propertiestoward a wide variety of normally tacky and pressure-sensitive adhesivesheet materials.

For many years manufacturers of inherently tacky mastics or adhesiveshave protected the compositions with such anti-stick, or "abhesive"material as wax-coated paper, plastic films, plastic-coated paper,starch-impregnated fabrics, and extremely complex polymer systems. Thelast-named type of polymer has found particular application as a coatingon the back surface of normally tacky and pressure-sensitive adhesivetape wound in roll form, where it functions as a so-called low adhesionbacksize (LAB), facilitating use of the tape and preventing inadvertenttransfer of the adhesive to the back surface. The force to separate thetape from an LAB coating typically ranges from 150 to 900 grams per inchof width, lower values generally causing roll instability and handlingproblems, and higher values making it excessively difficult to use thetape. For exemplary polymeric low adhesion backsizes, see U.S. Pat. Nos.2,532,011, 2,607,711, 2,876,894, 3,318,852, and 3,342,625.

For some products, e.g., labels or large adhesive-coated sheets sold inother than roll form, it is desirable to have a protective release linerto which normally tacky and pressure-sensitive adhesives adhere veryweakly; U.S. Pat. Nos. 3,230,289, 3,565,750, and 3,729,444 areillustrative of such products, all of which are based on a siliconecoating of some type. The force to separate a pressure-sensitiveadhesive from a silicone-treated surface is typically in the range of 10to 40 grams per inch of width, usually much too low for use as a lowadhesion backsize. Generally speaking, it has previously been almostimpossible to obtain materials having release properties intermediatethose of the LAB-type polymers and those of the silicones withoutsacrificing some other essential property.

Recognizing the desirability of a release coating having propertiesintermediate the 40 grams per inch shown by the extremely expensivesilicones and the 600 grams per inch shown by more modestly pricedtypical low adhesion backsizes, attempts have been made to modify thesilicone polymers by blending or reacting them with other less effectiverelease materials; see, e.g., U.S. Pat. Nos. 3,328,482, 3,723,566, and3,770,687. Some of the resultant modifications so contaminate apressure-sensitive adhesive that it loses its tack, while othersgradually react with a pressure-sensitive adhesive in such a manner thatthey cannot be separated after aging. Other compositions are difficultto reproduce with consistency, exhibit changed release properties as thesilicone gradually migrates to the surface, require cure temperatures sohigh that they adversely affect the substrate on which they are coated,or are effective only with a few specific adhesives.

SUMMARY OF THE INVENTION

The present invention provides, for the first time, it is believed, afamily of products which provide controllable release, or "abhesive"properties over the range represented by silicone polymers at the lowend and conventional low adhesion backsizes at the high end.

Products made in accordance with the invention are solid, crosslinked,substantially insoluble, joined interpenetrating polymeric networkreaction products of starting materials consisting essentially of (1) anisocyanate-terminated moiety and (2) an active hydrogen-containingorganosilicone moiety. The first moiety, which is liquid at 60° C. (andgenerally at 20° C.), is terminated with from more than 1 to less than 3isocyanate groups, has an NCO equivalent weight of at least about 100,and contains no more than 5 urea or urethane gram equivalents per 1000grams. Preferably the NCo groups are attached to aromatic rings. Thesecond moiety, which is liquid at 20° C., has a plurality of activehydrogen atoms each chemically bonded to a nitrogen or oxygen atom whichis at least three carbon atoms distant from the nearest silicon atom,the said oxygen or nitrogen atoms constituting no more than about 4% byweight of the organosilicone moiety. Preferably this moiety ispredominantly polydimethyl siloxane.

The stratum of release material made in accordance with the inventionmay be considered as a solid, crosslinked, substantially insolublepolymeric composition of matter consisting essentially of a producthaving the general formula

    (X.sub.m Y.sub.n).sub.p,

wherein

X is the residue of a polyisocyanate having an NCO equivalent weight ofat least about 100 and containing not more than 5 urethane or urea gramequivalents per 1000 grams,

Y is the residue of a liquid organosilicone having a plurality of activehydrogen atoms each bonded to a nitrogen or oxygen atom which is atleast 3 carbon atoms distant from the nearest silicon atom, saidnitrogen or oxygen atoms constituting no more than about 4% of theorganosilicone,

m, n and p are integers,

the ratio of n:m is no more than about 1.6:1, and

p is sufficiently great to cause said composition to be a solid.

The crosslinked reaction product can, in certain circumstances, beemployed as a completely self-supporting release sheet material, inwhich capacity it functions as a unique and comparatively inexpensivereplacement for the costly perfluoroolefin polymer films sometimes usedfor this purpose, exhibiting excellent tensile strength, tearresistance, heat resistance and solvent resistance; silicone polymerslack the strength, hardness, etc., to be used for this purpose withoutsome type of support. Sleeves, roll covers, and other shaped articleshaving release surfaces can be prepared. The product can similarly beemployed as a release liner if coated on one or both surfaces of paper,polymeric film, or similar substrates. Because of the ease in varyingthe release properties as desired, the invention permits coating tworelated but different compositions on opposite sides of a supportingsheet, thereby providing a liner having differential release properties.In other forms, the polymeric reaction product can be employed as an LABfor pressure-sensitive adhesive tape products, the specific releaseproperties being readily tailored to the value desired for the specifictape.

The reaction product is conveniently obtained by blending together in amutual solvent 98 to 50 parts by weight of the isocyanate-terminatedmoiety, 2-50 parts by weight of the previously described activehydrogen-containing liquid organosilicone moiety, and optionally acrosslinking agent such as a phenol-formaldehyde resin, coating theresultant pourable liquid in a thin layer, or stratum, upon a substrate,drying to remove the solvent, and, generally, heating the stratum toreact the moieties. The weights of the organosilicone and isocyanatemoieties are so selected that the mol ratio of the former to the latteris no more than about 1.6:1, the exact ratio being dependent upon themolecular weights of the two moieties, the presence or absence of acrosslinking agent, the hardness or release values desired, etc.

Typically the isocyanate-terminated moiety is prepared by theconventional process of reacting a stoichiometric excess of one or morepolyisocyanates with one or more diols, triols, diamines or triamines,thereby forming a prepolymer. Assuming all other factors are heldconstant, decreasing the molecular weight of the original polyol orpolyamine increases the hardness of the ultimate product attained uponreaction with the organosilicone. Exemplary polyols includepolyoxyethylene glycol, polyoxypropylene glycol, OH-terminatedpolyesters, 1,4-butane diol, 1,10-decane diol, OH-terminatedpolybutadiene, OH-terminated butadiene:acrylonitrile copolymers.OH-terminated butadiene:styrene copolymers, polytetramethylene etherdiol, glycerol, trimethylol propane, castor oil, etc. Exemplarypolyamines include ethylene diamine, diethylene triamine, hexamethylenediamine, polytetramethylene ether diamine, polyoxypropylene diamine,amine-terminated polyesters, etc. Because of lower cost, greateravailability and superior ease of handling, the polyols are generallypreferred.

Typical polyisocyanates for the preparation of prepolymers includetolylene diisocyanate, methylene bis(4-phenyl isocyanate), andpoly(phenylmethylene)triisocyanate, although others may be chosen forspecific purposes.

Preferably the active hydrogen-containing silicone moiety is asilane-modified polysiloxane. In preparing such moieties, linearpolysiloxane fluids, dimethyl- or predominantly dimethyl-substituted andfurther characterized by being hydroxyl-endblocked, are reacted withsilanes of the general formula

    R".sub.n (R'O).sub.3.sub.-n Si--W,

where

n is 0, 1 or 2, R" is a monovalent hydrocarbon radical containing from 1to 6 carbon atoms, R' is an alkyl radical containing from 1 to 4 carbonatoms and W is an aliphatic monovalent radical containing primary and/orsecondary amine groups, or carbinol groups. A preferred silane modifieris (CH₃ O)₃ Si(CH₂)₃ NH(CH₂)₂ NH₂, commercially available from DowCorning Corporation under the trade designation "Z-6020". Also usefulare silane-modified polysiloxanes such as that commercially availablefrom Dow Corning Corporation under the trade designation DC-531; suchproducts are also discussed in U.S. Pat. No. 3,508,933, as an additivefor automobile polish. The silane modification reaction is carried outin hydrocarbon solvents at slightly elevated temperatures in a systemfree of moisture.

DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

Throughout the remainder of the specification, all parts and percentagesare by weight unless otherwise noted.

In accordance with the invention, an isocyanate-terminated prepolymer isprepared as follows: Into a round bottom flask equipped with amotor-driven stirrer, reflux condenser, thermometer, and nitrogen gasinlet, there is introduced sufficient polyol to provide 0.05 hydroxylequivalent. Next there is introduced sufficient methyl ethyl ketonesolvent so that the total ultimate charge to the flask will contain 10%solids and 90% solvent. The stirrer is then turned on, sufficientpolyisocyanate added to provide 0.1 NCO equivalent, and the solutionbrought to reflux temperature (typically 80° C.) under a nitrogen purge.A 5% solution of lead octoate catalyst in methyl ethyl ketone is thenadded, approximately 0.1 gram catalyst per 100 grams of polyol plusisocyanate being employed. The reaction is then allowed to proceed atreflux under nitrogen purge for 3 hours, at the end of which time it isallowed to cool ambiently to room temperature and removed to a sealedstorage vessel.

Sheet material having release properties is prepared in accordance withthe invention as follows: Into a round bottom flask equipped with amotor driven stirrer and a nitrogen gas inlet is charged a sufficientquantity of the prepolymer prepared according to the preceding paragraphto provide the desired number of equivalents of NCO. The stirrer is thenturned on and, with the flask under a nitrogen purge, a sufficientquantity of a 10% solution of a suitable amine- or hydroxyl-containingsilicone is added to provide the desired number of amine or hydroxylequivalents. The reaction is then allowed to proceed for a predeterminedtime (typically from 1 to 24 hours), at the end of which time theproduct is removed from the reaction vessel and either stored in asealed container until needed or coated directly upon a desiredsubstrate. After coating, the solvent is then evaporated and thesubstrate optionally heated to react the isocyanate and amine orhydroxyl groups.

Although the mechanism of the reaction between the NCO-terminated moietyand the active hydrogen-containing silicone moiety is not fullyunderstood, the complex polymeric reaction product which is formedcontains new types of functionality, including urea, biuret andallophanic ester groups, while "locking in" the silicone segments withthe residue of the isocyanate-terminated moiety. The reaction product isproperly classified as a "joined interpenetrating polymer network" asopposed to a block copolymer; cf. Sperling, ACS Polymer Preprints, Vol.14(2), August, 1973. (In this regard, attention is further directed toU.S. Pat. No. 3,705,823, which describes fibrous structures coated withthe block copolymer reaction product of certain polyurethane prepolymersand certain polyorganosiloxanes.) If desired, a polyfunctionalcrosslinking agent such as N,N,N',N'-tetra(2-hydroxypropyl)ethylenediamine or a phenol-formaldehyde resin may be introduced into thereaction mixture to impart greater hardness or further reduce adhesionof pressure-sensitive adhesives to the surface of the reaction product.

The exact coating technique is not especially critical, and any ofseveral well known procedures may be followed. It has been found,however, that a rotogravure applicator roll having 200 lines per inchprovides a uniform and effective means of applying a 10% solution of theisocyanate-terminated prepolymer and active hydrogen-containingsilicone. Wire-wound rods, such as a Mayer bar, are likewise effectivefor this purpose.

Certain tests have been found helpful in evaluating the effectiveness ofrelease liners or low adhesion backsize coatings. For convenience, thesetests and their significance are described in subsequent paragraphs.

Release

A strip of the test tape 1 inch wide × 10 inches long is applied to astrip of sheet material (prepared in accordance with the invention)11/2inches wide × 10 inches long and rolled down with one pass of a41/2-pound rubber-covered roller. One end of this liner-tape compositeis attached, by means of a clamp and hook arrangement, to a point on thelower periphery of a horizontal, three-inch diameter aluminum cylinderwhich is located in an oven. The liner-tape composite is then loopedover the cylinder, tape-side out, and a 500 gram weight attached to tothe other end. While thus under stress, the composite is then aged for16 hours at 150° F.¹, after which it is removed to a 72° F., 50%relative humidity environment for about 2 hours. "Stripback" adhesionvalue is then obtained by wrapping the composite tape-side out, around a3-inch diameter free-turning spindle, and stripping the tape away fromthe liner at a 90° angle at 90 inches per minute while measuring thestripping force in grams or ounces per inch of width.

An effective release liner should provide a stripping force of no morethan 150 grams per inch of width, even with extremely aggressiveadhesives. Preferably this value should not exceed 100 grams per inch,and for many adhesives it will be less than 30 grams per inch. Thesevalues are particularly important in the case of wide strips of easilystretchable tape, which may otherwise become badly distorted duringremoval from the liner. For a low adhesion backsize release coating, therelease value in accordance with this test should be in the range of150-900 grams per inch of width.

Adhesion loss

To determine whether the liner deleteriously affects the adhesive, astrip of tape, aged as described above, is removed from the liner,applied to a clean glass surface, rolled down with one pass of a4-1/2-pound rubber roller, and stripped from the glass at a 180° angleat 90 inches per minute while measuring the adhesion value in ounces.This value is compared to that obtained using as a control the same tapewhich has been kept out of contact with the liner. Assuming that theadhesive is not adversely affected by heat alone, the adhesion to glassafter aging should be at least 80% of the control. If part of theliner's adhesive-contacting surface transfers to or reacts with theadhesive, this percentage will be significantly lower.

Unwind force

A roll of tape 1/2 inch wide is mounted so as to be freely rotatableabout a shaft which in turn is mounted on a bracket attached to amovable carriage. The free end of the tape is gripped between the jawsof a device capable of recording tensile force, and the carriage is thenmoved away from the jaws at the rate of 90 inches per minute. The unwindforce is noted and reported as either ounces or grams per inch of width.An effective low adhesion backsize coating will permit the tape to beunwound with a force of at least about 150 grams per inch of width butgenerally not more than about 900 grams per inch of width.

Subsequently appearing Tables I and II show products made by preparingisocyanate-terminated prepolymers (or directly usingisocyanate-terminated moieties), mixing them with amine-orhydroxyl-containing silicones (and optionally phenolaldehyde resincrosslinking agent), coating the mixture on a 2-mil biaxially orientedpolyethylene terephthalate film, heating to react the variouscomponents, and thereafter measuring the characteristics of the surfaceof the cured reaction product when placed in contact with tapes havingtwo different types of normally tacky and pressure-sensitive adhesives*.Preparation and testing procedures were as previously described. In theexamples, the following abbreviations are employed:

    ______________________________________                                        Prepolymer polyol bases                                                       1,4           1,4-butanediol                                                  1,10          1,10-decanediol                                                 ACN           OH-terminated butadiene:acrylonitrile                                         copolymer having an average molecular                                         weight of 2400, available from                                                Sinclair-Koppers Co. under the trade                                          designation "Poly B-D CN-15"                                    PD            OH-terminated polybutadiene resin                                             having an average molecular weight                                            of 3200, available from Sinclair-                                             Koppers Co. under the trade designa-                                          tion "Poly B-D R-15M"                                           CAB           Alcohol-soluble cellulose acetate                                             butyrate resin containing an average                                          of 47% butyryl, 1.6% acetyl, and                                              4-5% hydroxyl                                                   CAST          Castor oil                                                      DANT          Di(2-hydroxyethyl)dimethylhydantoin,                                          commercially available from Glyco                                             Chemicals, Inc. under the trade                                               designation "Dantocol"                                          P 52          Poly bis-hydroxy ethyl azelate,                                               commercially available from Emery                                             Industries, Inc. under the trade                                              designation "Polyester 3752-D"                                  PCLD          Polycaprolactone diol, having an                                              average formula molecular weight of                                           530, commercially available from                                              Union Carbide Corporation under                                               the trade designation "Niax Polyol                                            D-510"                                                          PG 200        Tris(hydroxypropyl) glycerine,                                                commercially available from The Dow                                           Chemical Company under the trade                                              designation "Voranol CP-260"                                    PG 400        Polyoxypropylene glycol having an                                             OH number of about 265, commercially                                          available from Union Carbide                                                  Corporation under the trade des-                                              ignation "PPG-425"                                              PG 500        Polyoxypropylene glycol having an                                             average molecular weight of about                                             490, commercially available from                                              Union Carbide Corporation under the                                           trade designation "LS-490"                                      PG 700        Polyoxypropylene glycol having an                                             average molecular weight of about                                             775, commercially available from                                              Wyandotte Chemical Corporation under                                          the trade designation "Pluracol P 710"                          PG 2000       Polyoxypropylene glycol having an                                             average molecular weight of about                                             2000, commercially available from                                             Union Carbide Corporation under the                                           trade designation "PPG-2025"                                    PG 4000       Polyoxypropylene glycol having an                                             average molecular weight of about                                             4200, commercially available from                                             Union Carbide Corporation under the                                           trade designation "LHT-42"                                      Isocyanates                                                                   PAPI          Polymethylene polyphenyl isocyanate,                                          commercially available from Upjohn                                            Company under the trade designation                                           "PAPI 901"                                                      ISO           Similar to "PAPI," commercially                                               available from Upjohn Company under                                           the trade designation "Isonate 390-P"                           MRS           Similar to "PAPI," commercially                                               available from Mobay Chemical                                                 Company under the trade designation                                           "Mondur MRS"                                                    TDI           Tolylene diisocyanate                                           Crosslinking agent                                                            Phen          Heat-advancing, oil soluble phenol-                                           aldehyde resin, commercially available                                        from Union Carbide Corporation under                                          the trade designation "CKR 1634"                                Silicones                                                                     A             Polydimethyl siloxane having both                                             primary and secondary amine groups                                            on pendent side chains, at least 3                                            carbon atoms removed from the nearest                                         silicon atom, commercially available                                          from Dow Corning Corporation under                                            the trade designation "DC-531"                                  B             Polydimethyl siloxane having secondary                                        amine groups on pendent side chains,                                          at least 3 carbon atoms removed from                                          the nearest silicon atom, commercially                                        available from Dow Corning Corporation                                        under the trade designation "XF-3655"                           C             Polydimethyl siloxane similar to "A,"                                         commercially available from Dow                                               Corning Corporation under the trade                                           designation "XF-3656"                                           D             Polydimethyl siloxane with pendent                                            primary amine groups [(CH.sub.2).sub.4 NH.sub.2 ],                            commercially available from Union                                             Carbide Corporation under the trade                                           designation "Y-6165"                                            E             Polydimethyl siloxane similar to "D,"                                         commercially available from Union                                             Carbide Corporation under the trade                                           designation "Y-5477"                                            F             Reaction product of 94 mols dimethyl                                          siloxane and 6 mols methyl phenyl                                             siloxane, having an OH equivalent                                             value of 18,000                                                 G             Reaction product of 10 parts "F" and                                          1 part N-βaminoethyl)-γaminopropyl                                 trimethoxysilane                                                H             Reaction product of 10 parts "F"                                              and 1 part (CH.sub.3 O).sub.3 Si(CH.sub.2).sub.3 NH(CH.sub.2                  ).sub.2 NH(CH.sub.2).sub.2                                                     ##STR1##                                                       ______________________________________                                    

                  TABLE I                                                         ______________________________________                                                                        Parts                                                                         phenolic                                      Polyurethane prepolymer                                                                             Silicone  Cross-                                        Example                                                                              Base     Isocyanate                                                                              Parts Type Parts                                                                              linker                              ______________________________________                                        1      1,4      PAPI      97.7  A     2.3 32                                  2       "       "         83.3  "    16.7 16.7                                3       "       "         62.5  "    37.5  7.5                                4       "       "         25.0  "    75.0  5                                  5      BD       "         82.6  "    17.4 17.4                                6      ACN      "         "     "    "    "                                   7      PG 4000  "         81.8  "    18.2  6.7                                8      DANT     "         75.0  "    25.0 12.5                                9      PG 400   "         66.7  "    33.3 33.3                                10     P 52     "         50.0  "    50.0 10.0                                11      --      ISO       5.0   "    95.0  0                                  12     CAB      TDI       83.3  "    16.7  0                                  13     CAST     "         50.0  "    50.0 25.0                                14     1,10-    MRS       63.7  "    36.3  9.1                                15     1,4-     PAPI      75.6  B    24.4 12.2                                16       "      "         "     C    "    "                                   17      "       "         72.2  D    27.8 13.9                                18      "       TDI       80.0  E    20.0 20.0                                19     P 52     PAPI      66.7  G    33.3  0                                  20      "       "         33.3  H    66.7  0                                  ______________________________________                                    

                  TABLE II                                                        ______________________________________                                                         Adhesion to                                                  Release          glass after heat                                             gms/in           aging, oz/in. Satisfac-                                                Rubber-         Rubber-  tory for                                          Acrylic  resin    Acrylic                                                                              resin  LAB  Liner                             Example                                                                              adhesive adhesive adhesive                                                                             adhesive                                                                             ?    ?                                 ______________________________________                                        1      570      740      48     84     Yes  No                                2       30      140      44     70     No   Yes                               3       30      160      42     68     No   Yes                               4      160      220      50     88     Yes  Some                                                                          adhe-                                                                         sives                             5      100      100      44     49     No   Yes                               6       80      210      53     57     Some Some                                                                     adhe-                                                                              adhe-                                                                    sives                                                                              sives                             7      250      1140     40     52     Some Some                                                                     adhe-                                                                              adhe-                                                                    sives                                                                              sives                             8       30      140      44     69     No   Yes                               9       30       60      52     48     No   Yes                               10      30      140      40     49     Some Yes                                                                      adhe-                                                                         sives                                  11     140      180      42     71     Some Mar-                                                                     adhe-                                                                              ginal                                                                    sives                                  12     220      140      43     52     Yes  Some                                                                          adhe-                                                                         sives                             13      30      160      50     48     Yes  No                                14      50       80      49     73     No   Yes                               15     500      720      48     45     Yes  No                                16     140      200      54     74     Yes  No                                17     140      390      50     84     Yes  No                                18     140      320      48     60     Yes  No                                19     100      150      41     76     Some Yes                                                                      adhe-                                                                         sives                                  20      20       70      44     64     No   Yes                               ______________________________________                                    

Examples 21-31 tabulated in Tables III and IV below, show thepreparation of tape products having a low adhesion backsize inaccordance with the invention. In preparing both the prepolymer and thefinal polymer, the equivalent weight of each reactant was preciselydetermined by titration. Preparation techniques were essentially thesame as in previous examples. The tape backing to which the low adhesionbacksize coatings were applied was one-mil biaxially orientedpolyethylene terephthalate. Thereafter, the other side of the backingwas coated with two different normally tacky and pressure-sensitiveadhesives, an "acrylate adhesive" and a "rubber-resin adhesive". Theformer was a 96:4 isooctyl acrylate: acrylamide copolymer, as describedin U.S. Pat. No. Re. 24,906. The latter was formulated from 100 partsmilled pale crepe rubber tackified with 75 parts of polymerized b-pinenehaving a softening temperature of 115° C., and containing an alkylatedphenol antioxidant. Figures reported in Table IV are the average forthree rolls of tape taken from the left, right and center of a wideroll.

                                      TABLE III                                   __________________________________________________________________________                                          Final polymer                           NCO-terminated prepolymer             Parts      NCO:                                                                              Reac-                         Equivalents                                                                          Equivalents   Equivalents                                                                          NCO  NCO-  Parts                                                                              NH.sub.2                                                                          tion                          1,4-   PG     Equivalents                                                                          polyiso-                                                                             equiva-                                                                            terminated                                                                          Silicone                                                                           mol time,                    Example                                                                            butane-diol                                                                          700    PG 2000                                                                              cyanate                                                                              lent wt.                                                                           prepolymer                                                                          "A"  ratio                                                                             hours                    __________________________________________________________________________    21   20     80     --     200    776  75.4  24.6 11:1                                                                              1                        22   50     50     --     "      "    75.2  24.8 11:1                                                                              1                        23   "      "      --     "      526  64.4  35.6  9:1                                                                              1                        24   "      "      --     "      "    "     "    "   24                       25   "      "      --     "      "    48.5  51.5  5:1                                                                              1                        26   "      "      --     "      "    "     "    "   24                       27   80     20     --     "      857  77.2  22.8 11:1                                                                              1                        28   --     --     100    "      4390 57.5  42.5   4:1                                                                             1                        29   --     --     "      "      "    64.9  35.1 11:1                                                                              1                        30   50     --      50    "      704  52.0  48.0  4:1                                                                              1                        31   "      --     "      "      "    74.8  25.2 11:1                                                                              1                        __________________________________________________________________________

                                      TABLE IV                                    __________________________________________________________________________    Acrylate adhesive            Rubber-resin adhesive                            Unwind force,    Adhesion to glass,                                                                        Unwind force,                                                                             Adhesion to glass,                   grams/inch       oz./inch    grams/inch  oz./inch                             Example                                                                            Initial                                                                            After aging                                                                          Initial                                                                            After aging                                                                          Initial                                                                            After aging                                                                          Initial                                                                           After aging                      __________________________________________________________________________    21   60   310    54   58      60  310    54  62                               22   "    60     54   62      60  170    58  60                               23   "    310    42   50     170  280    46  48                               24   "    60     46   48     170  510    54  58                               25   "    "      42   50     170  280    50  54                               26   "    "      50   46     170  480    50  58                               27   570  split  52   split  280  960    55  54                               28   60   60     58   50     170  170    66  62                               29   "    "      62   60     280  280    62  66                               30   "    "      58   54     170  280    62  66                               31   "    "      62   58     280  280    62  62                               __________________________________________________________________________

While the products of previous examples were inherently capable of beingformed into self-supporting strata for use as heat-resistant releaseliners, the next two examples expressly disclose the preparation ofself-supporting films of this type. In each case, anisocyanate-terminated prepolymer was prepared by reacting astoichiometric excess of TDI with PCLD diol. Next 30.0 parts of theprepolymer (50% solids in methyl ethyl ketone) 20.0 parts of phenolicresin crosslinker and 5.0 parts PG 500 (the latter two as 50% solidssolution in xylene) were reacted for either one hour (Example 32) ortwenty hours (Example 33).

In both Example 32 and 33, 88.2 parts of the appropriate reactionproduct solution (see preceding paragraph) was mixed with 11.8 partssilicone A solution. Films were then cast by pouring a thin layer of themixed solutions into a Teflon perfluoroolefin-lined flat-bottom pan, andthe solvent allowed to evaporate overnight at room temperature and theremaining solid materials heated in an oven at 300° F. (about 150° C)for 5 minutes. The film, approximately 10 mils (250 microns) thick ineach case, was then removed from the pan and subjected to variousphysical tests, with the results tabulated below:

                  TABLE V                                                         ______________________________________                                                          Release, gms/in. width                                             Tensile   % elonga-  Acrylic                                                                              Rubber-resin                               Example                                                                              strength, psi                                                                           tion at break                                                                            adhesive                                                                             adhesive                                   ______________________________________                                        32     4266       1.3       32     44                                         33     1134      75.8       87     40                                         ______________________________________                                    

It will be appreciated that the foregoing description does not purportto cover all the ramifications of this invention. Using the principlesdisclosed, however, those skilled in the art will be able to modify,adapt and employ the invention to fit specific situations.

What is claimed is as follows:
 1. A pressure-sensitive adhesive tape inwhich a sheet backing is provided, on one surface, with a layer ofnormally tacky and pressure-sensitive adhesive and on the other surfacewith a low adhesion backsize which isthe solid, crosslinked,substantially insoluble joined interpenetrating polymeric networkreaction product of starting materials consisting essentially of (1)98-50 parts by weight of a first moiety terminated with from more than 1to not more than 3 isocyanate groups, liquid at 60° C., having an NCOequivalent weight of at least about 100, containing not more than 5urethane or urea gram equivalents per 1000 grams of said moiety, andformed by reacting one or more polyisocyanates with one or more diols,triols, diamines or triamines, and (2) correspondingly 2-50 parts byweight of an organosilicone second moiety which is a silane-modifiedOH-endblocked predominantly dimethyl-substituted linear polysiloxane, isliquid at 20° C., and has a plurality of active hydrogen atoms eachchemically bonded to a nitrogen or oxygen atom attached to a CH₂ groupwhich is at least 3 carbon atoms distant from the nearest silicon atom,said nitrogen or oxygen atoms constituting no more than about 4% byweight of said organosilicone moiety.
 2. A removable release liner inwhich a sheet backing is provided, on at least one surface, with a thinrelease layer which isthe solid, crosslinked, substantially insolublejoined interpenetrating polymeric network reaction product of startingmaterials consisting essentially of (1) 98-50 parts by weight of a firstmoiety terminated with from more than 1 to not more than 3 isocyanategroups, liquid at 60° C., having an NCO equivalent weight of at leastabout 100, containing not more than 5 urethane or urea gram equivalentsper 1000 grams of said moiety, and formed by reacting one or morepolyisocyanates with one or more diols, triols, diamines or triamines,and (2) correspondingly 2-50 parts by weight of an organosilicone secondmoiety which is a silane-modified OH-endblocked predominantlydimethyl-substituted linear polysiloxane, is liquid at 20° C., and has aplurality of active hydrogen atoms each chemically bonded to a nitrogenor oxygen atom attached to a CH₂ group which is at least 3 carbon atomsdistant from the nearest silicon atom, said nitrogen or oxygen atomsconstituting no more than about 4% by weight of said organosiliconemoiety.
 3. The liner of claim 2 wherein each of the two surfaces of thesheet backing is provided with a thin release layer, the two layersexhibiting different release properties.
 4. The method of making aself-supporting sheet material capable of being wound convolutely uponitself in roll form, said sheet material affording accuratelypredictable and controllable release for a wide variety of normallytacky and pressure-sensitive adhesives, which method includes the stepsof:a. blending together in a mutually compatible solvent systemcomponents consisting essentially of1. 98-50 parts by weight of a firstmoiety terminated with from more than 1 to not more than 3 isocyanategroups, liquid at 60° C., having an NCO equivalent weight of at leastabout 100, containing not more than 5 urethane or urea gram equivalentsper 1000 grams of said moiety, and formed by reacting one or morepolyisocyanates with one or more diols, triols, diamines or triamines,and
 2. correspondingly 2-50 parts by weight of a second organosiliconemoiety which is a silane-modified OH-endblocked predominantlydimethyl-substituted linear polysiloxane, is liquid at 20° C. and has aplurality of active hydrogen groups each chemically bonded to a nitrogenor oxygen atom attached to a CH₂ group which is at least 3 carbon atomsdistant from the nearest silicon atom, said active hydrogen bearingatoms constituting no more than about 4% by weight of saidorganosilicone moiety, thereby forming a pourable liquid, b. coating thepourable liquid in a thin stratum upon a substrate, c. drying to removethe solvent, and d. reacting the moieties.
 5. The method of claim 4wherein the components additionally include a crosslinking agent.
 6. Themethod of claim 4 wherein the crosslinking agent is a phenolic resin. 7.The method of claim 4 wherein the organosilicone moiety is the reactionproduct of a hydroxyl end blocked polydimethylsiloxane and a silaneselected from the group consisting of those having the structuralformula

    R".sub.n (R'O).sub.3.sub.-n SiRNHCH.sub.2 CH.sub.2 NH.sub.2,

wherein R" is a monovalent hydrocarbon radical free of aliphaticunsaturation and containing from 1 to 6 carbon atoms, n has a value from0 to 2, R' is an alkyl radical containing from 1 to 4 carbon atoms, R isa divalent hydrocarbon radical free of aliphatic unsaturation andcontaining 3 to 4 carbon atoms, the siloxane:silane weight ratio is inthe range of about 1:1 to 20:1.
 8. The method of claim 7 wherein thesilane is (CH₃ O)₃ Si(CH₂)₃ NH(CH₂)₂ NH₂.
 9. The method of claim 7wherein the silane is ##STR2##